This invention relates to electroless gold plating solutions containing boron-based reducing agents.
There are known electroless gold plating solutions containing potassium gold cyanide, potassium cyanide, and potassium hydroxide and having an alkalimetal borohydride or alkylamine borane such as dimethylamine borane added as a reducing agent (see PLATING, September 1970, pages 914-920). These solutions autocatalytically produce electroless gold plated films which are substantially free of boron and thus pure and sound. The solutions are conveniently used in gold plating electronic parts or the like.
The conventional electroless gold plating solutions of this type, however, are not practical because of their slow deposition rate of the order of 0.5 .mu.m per hour. It is strongly desired to solve the problem of slow deposition.
One solution is to add lead to accelerate deposition rate as disclosed in Japanese Patent Application Kokai No. 60-121274. Insofar as we have studied, the addition of lead not only gives rise to other problems in appearance of gold plated films and covering or throwing power, but also results in gold plated films with substantially deteriorated color tone and a steep decline of deposition rate particularly when lead is added in amounts of 10 ppm (parts per million parts) or more.